That makes me wonder if he thought someone might be eavesdropping. Maybe they'd planned before ever stepping foot in Karda Nui to speak as if they wanted to kill the Toa and never let on otherwise just in case a spy might report the content of their internal meetings to the Toa.
Why would he think that, though. Both sides were regrouping at the time, and after Kirop was so easily fooled by the Toa Nuva, I'm sure they were careful not to let any Matoran near the meeting.
Unfortunately, I think if GregF were to be asked about this, he'd probably just say he couldn't remember. I think it was either to throw off the reader, or GregF forgot what the Makuta's priorities would have been when he was writing it.
If it was intentional though, and the Makuta had ensured that only Brotherhood members were present, why would he have said that, and why would Vamprah have been trying to kill Lewa?
As for Icarax, it's quite obvious why he attacked Ignika. He thought it was simply a toa wearing the mask, not the mask itself with the body of a toa. In that case, Ignika far overpowered the villains, but I'm more or less talking about the Toa Nuva than Ignika. Icarax already knew he could defeat the Toa Nuva one-on-six, and he had no reason to hold back. If self-preservation was his reason, then why didn't he just fly back to Destral? I see no reason why Icarax would have held back any of his powers, and I'm certain a Makuta like him would have had no problem fighting through the pain of Ignika's curse. At most, it was just a minor hindrance, unlike the Phantoka Makuta's blindness. He still had all of his powers short of shapeshifting, and he could see. Forty-one options at his disposal, and yet he never actually accomplished any major feat when in karda Nui.